Flywheel/Clutch energy loss 3

[RobertCasey]

I am looking at designing a system that uses a flywheel to accelerate a secondary mechanical system to a required speed via a clutch. The clutch is gradually closed so that the secondary system is accelerated smoothly. Once the secondary system has reached a set speed, the clutch will open.

The energy lost from the flywheel will consist of the energy required to accelerate the secondary system (I am assuming a constant acceleration), plus energy in heat loss in the clutch.

My problem is that I dont know how I can calculate this heat loss energy. Can anyone give me any info about how I can tackle this, or any pointers to web sites or books that might be useful.

Thanks

 

[ve7brz]

I can't answer your question regarding the calculation of losses due to heating, but you'll find an efficient mechanism mentioned in this thread: 404-35775.

 

[RichLeimbach]

Robert,
I have found this situation to be described very well with the Law of Conservation of Angular Momentum. You can find more out on this in most any physics book, but the basics are:

Angular momentum is conserved during any engagement of rotating objects (regardless of engagement speed). The heat energy generated at the engagement is determined by the difference in starting and ending KEs of the system and is almost exclusively controlled by the inertias of the object and the starting velocities of both parts. I have found this to be true as long as the external forces acting on these objects during the same time period are negligible.

The math behind it is:

Starting angular momentum = I1*w1

Starting energy = 1/2*I1*w1^2 (plus energy in I2 which is in this case zero)

After engagement speed is w2= (w1*I1)/(I1+I2)

Kenetic energy after engagement = 1/2*(I1+I2)*w2^2

Losses (heat) during engagement = KE (starting) - KE (final)

Hope this helps.

- Rich

 

[ve7brz]

Good one Richard!

Bruce

 

[RobertCasey]

Thanks Rich! Your advice was very helpful. I found out that my application would expend 52MJ of energy during the 3 seconds clutching time - so a vapourised clutch! Back to the drawing board...

 

[RichLeimbach]

Robert,

Holy Smokes!! That's a lot of energy. What is the application?

From my experience, you can make some nice gains on this number if you either: 1. Increase flywheel mass, 2. Decrease driven mass or 3. Decrease differential in speed between the two parts.

Not sure if you'll be able to get it into the right range or not, but good luck.

-Rich

 

[RobertCasey]

The application is for an amusement device so the driven loads and the speed cannot be varied. However, by increasing the mass of the flywheel I can get the energy loss down to 16MJ which is a lot better (but now I've got a huge flywheel which I think will be very expensive to fabricate and balance) so I suspect I need to to look at another solution. Thanks for your help anyway!